ENH: Use gridname as name for simulator_fipregions_mapping

[tnatt]

Resolves #1633

Checklist

• Tests added (if not, comment why)
• Test coverage equal or up from main (run pytest with --cov=src/ --cov-report term-missing)
• If not squash merging, every commit passes tests
• Appropriate commit prefix and precise commit message used
• All debug prints and unnecessary comments removed
• Docstrings are correct and updated
• Documentation is updated, if necessary
• Latest main rebased/merged into branch
• Added comments on this PR where appropriate to help reviewers
• Moved issue status on project board
• Checked the boxes in this checklist ✅

[HansKallekleiv]

That was fast :)
From a consumer perspective I guess this is more or less on hold until the relevant mapping from modelling grid to simulation grid is in place?

[tnatt]

Will put this on hold until we have specked out how to do the mapping of a rms grid name to a eclipse grid name. Most likely fmu settings can be of use here.